The present invention relates to a beam splitting optical element which divides an incident beam into a plurality of number of emitted beams, and more particularly, to a beam splitting optical element using diffractive gratings.
Conventionally, beam splitters using diffractive gratings have been known. In such beam splitters, linear grooves or raised portions (i.e., gratings) are formed on, for example, a glass substrate. The arrangement of the gratings determines the pattern of emitted diffracted beams. Typically, the emitted beams (.+-.1st order beams, .+-.2nd order beams, . . . ) are arranged symmetrically around a central beam (i.e., a zero order diffracted beam) and, as a result, there are an odd number of diffracted beams emitted.
A diffraction efficiency of the conventional diffractive gratings as described above is generally in a range of 70%-85%. There is need for a beam splitter employing diffractive gratings which has a relatively high diffraction efficiency.
Further, in the field of digital opto-electronics, it is particularly useful if a diffractive optical element has an even number of emitted beams having relatively similar intensities. For example, in an optical recording device accessed by a computer or an optical computer, eight bits (a byte) is a unit when data is processed. If a beam is divided into an even and desired number of beams by the beam splitter, it is advantageous since the emitted beams are used for processing the data efficiently.